The present invention relates, in general terms, to the art of forming fibers from a relatively thick stream of molten thermoplastic material. More particularly, the invention is concerned with the production of mineral fibers or mineral wool, for instance glass fibre insulation.
The production of mineral wool, particularly glass wool, is an important industrial field particularly due to the universally acknowledged significance of proper thermal insulation. High insulating properties, low weight and as inexpensive production as possible are obvious requirements in producing the satisfactory results.
It is well known that an ideal mineral wool would have as uniform a diameter of the fibers as possible. Furthermore, it is a requirement that the content in the wool of "shot", i.e. small solidified droplets of unfiberized material be as low as possible. It is generally acknowledged that the average diameter of the glass fiber in mineral wool should be within the range of 4-13 microns.
Mineral wool is known to be produced from a relatively thick primary stream of molten material which is subjected to different mechanical processes directed to firstly subdivide the thick stream into a plurality of relatively narrow streamlets having a smaller diameter, whereupon the material of each streamlet is subjected to attenuation usually effected by attenuating drums or the like. The use of hot air in providing the final attenuation of the formed fibers and also to remove the formed fibers from the attenuation drums or the like is also a well known practice.
The first group of prior art to which reference may be had discloses a process in which molten mineral material such as glass is applied to fiberizer drum surfaces in the form of a thick stream or streams or also in the form of large droplets which then bounce from drum to drum. The object of the arrangement is to distribute the glass uniformly over the fiberizing surfaces of the drums. The application process may also be enhanced by the use of a textured distributor role. U.S. Pat. No. 2,520,168 issued Aug. 29, 1950 to E. R. Powell, U.S. Pat. No. 3,159,475 issued Dec. 1, 1964 to A. B. Chen et al. and U.S. Pat. No. 2,758,335 issued Aug. 14, 1956 to E. R. Overman et al. present each a typical arrangement utilizing a thick stream distributed by a series of drums. A distributor disk co-operating with fiberizing drums or disks is known to enhance the acceleration and spread of the molten glass. U.S. Pat. No. 2,774,103 issued Dec. 18, 1956 to B. A. Graybeal and U.S. Pat. No. 2,577,431 issued Dec. 4, 1951 to E. R. Powell presents one embodiment wherein a distributor disk is disposed generally centrally of a series of fiberizing disks of larger diameter. Another enhancement device directed to facilitate the distribution of the thick stream of molten glass is shown in U.S. Pat. No. 2,577,431 issued Dec. 4, 1951 to E. R. Powell. In the last mentioned patent, the application enhancement device is formed by a gas jet. It is further known from the above U.S. Pat. No. 2,520,168 that if the additional stream of molten material is split in two, an additional spreading effect takes place.
It has been discovered that the mode of essentially random application of molten glass to the surface of rotating drums or disks as shown by the above prior art references results in an unsatisfactory uniformity of distribution of glass with the result that a relatively large proportion of the glass material is unfiberized.
It is further known to use so called "slinger cup" disclosed, for instance, in U.S. Pat. No. 4,111,673 issued Sept. 5, 1978 to Van Natta or U.S. Pat. No. Re. 25,306 issued Dec. 25, 1962 to J. Corsentino. The concept of the slinger cup is different from the application drums in that the slinger cup actually holds in a annular cavity in its upper face portion a volume of molten material. As the cup rotates, the material from within the cup is centrifugally forced through notches in the upper edge of the peripheral rim of the cup, thus forming a relatively thin streamlets of molten glass. The streamlets are then subjected to a blow by hot air which provides the attenuation effect. The disadvantage in the combination of a slinger cup and hot air blow is seen in that the slinger cup has to produce a relatively fine stream of molten glass. In order to assure reasonable production capacity, a high speed of the slinger cup is required to obtain the desired small diameter of the final fiber. In actual operation, therefore, the slinger cup requires very high speed of rotation and the uniformity of attenuation by blowing hot air over the formed fibers is still somewhat non-uniform.